1. Field of the Invention
The present invention relates to a flame-retardant aromatic co-polyester composition. More particularly, it is concerned with a flame-retardant aromatic co-polyester composition comprising a halogen-free aromatic co-polyester and a halogen-containing aromatic co-polyester.
2. Description of the Prior Art
Aromatic co-polyesters comprising isophthalic acid, terephthalic acid and 2,2-bis(4'-hydroxyphenyl) propane are well known. It is also known that such aromatic co-polyesters possess excellent mechanical and electrical properties and have excellent heat resistance and solvent resistance.
Such aromatic co-polyesters are mainly used in the mechanical field and in the electrical field due to their excellent mechanical and electrical properties, excellent heat resistance, and solvent resistance. However, their flame-retardant capabilities are not completely satisfactory.
It is also known to incorporate a phosphorus-containing compound, a halogen-containing compound, a metal compound, or the like in aromatic co-polyesters in order to render them flame-retardant. However, these compounds have poor heat stability at elevated temperatures and, when subjected to melt-molding (for example, extruding to obtain pellets) or injection molding, they undergo decomposition and deteriorate the inherent properties of the aromatic co-polyesters themselves.
Halogen-containing aromatic co-polyesters comprising isophthalic acid, terephthalic aicd and 2,2-bis(4'-hydroxy-3',5'-dibromophenyl)propane and/or 2,2-bis(4'-hydroxy-3',5'-dichlorophenyl)propane are also well known. Such halogen-containing aromatic co-polyesters have excellent electrical properties, heat stability, solvent resistance and, in particular, excellent flame-retardant capabilities. However, with bisphenols where the position ortho to the hydroxy group is substituted by a halogen, polymers of excellent mechanical properties are difficult to obtain due to the comparative difficulty in obtaining high molecular weight polymers.
Halogen-conaining aromatic co-polyesters comprising isophthalic acid, terephthalic acid and 2,2-bis(4'-hydroxyphenyl)propane and 2,2-bis(4'-hydroxy-3',5'-dibromophenyl)propane and/or 2,2-bis(4'-hydroxy-3',5'-dichlorophenyl)propane are also known due to their excellent electrical properties, heat stability and solvent resistance. Above all, such materials exhibit excellent flame-retardant capabilities. However, high molecular weight copolymers are difficult to obtain when the proportion of 2,2-bis(4'-hydroxy-3',5'-dibromophenyl)propane and/or 2,2-bis(4'-hydroxy-3',5'-dichlorophenyl)propane to total bisphenols is increased. Thus, the mechanical properties of resulting copolymers are poor.
As a result of extensive research on processes to impart flame-retardant capabilities to the aforesaid halogen-free aromatic co-polyesters without deteriorating the excellent mechanical and electrical properties thereof, the inventors achieved the present invention.